Re: [Haskell-beginners] netwire and "dynamic" list of objects

10 Apr 2012

      Firstly, thanks for the answer.

Ok, I made another attempt. I have a function, to output the state of
one object:

objectWire :: StdGen -> MyWire () ObjectState

The random generator is used to create the initial state. Now I want to
handle a dynamic set of objects. This is my attempt:

wire :: MyWire () State
wire = proc _ -> do
     rec
       rnds <- Wire.delay initRnds -< (tail rnds)
     let rnd = head rnds        --Get a fresh random generator everytime
     --For now, only one new object every call
     let newObjWires = [objectWire rnd]
     rec
       --Start with newObjWires and add newObjWires everytime (1. Error)
       objWires <- Wire.delay newObjWires -< newObjWires ++ objWires

     oss <- distribute objWires -< () -- 2. Error
     Wire.identity -< GameState rnds ss
     where
       initRnds = stdgens $ mkStdGen 0

Now I get
Not in scope: `newObjWires'
at the 1. Error and
Not in scope: `objWires'
at the 2. Error.

OK, I am guessing that I may not use newObjWires/objWires as parameters
to the functions creating the wires.
But I do not understand how to use any of Control.Wire.Trans.Combine to
handle my dynamic set of wires.

Regards,
Nathan

On 04/10/2012 01:57 PM, Ertugrul Söylemez wrote:
...
Nathan Hüsken  wrote:
...
I have a simple SDL based graphic demo, which I am trying (for
educational purposes) to rewrite utilizing netwire.
The demo basically consists of a State which contains a list of object
states.
[...]
But I avoided rewriting "updateState" in wire format. But I have no
Idea how to do that.
How do I handle a dynamic list of objects in a wire?
Well, you are not really using FRP here.  You are just forcing this
application into the FRP model.  Your only behavior is the application
itself.  This works, but buys you nothing.
The first step to actually making use of FRP here is to get rid of the
concept of "updating" something.  Express your game objects themselves
as wires:
player :: GameWire (Input, [Wall]) Player
    wall   :: GameWire a Wall
    enemy  :: GameWire (Player, [Wall]) Enemy
This allows you to write static game worlds.  After that you can move to
dynamic game worlds using wire transformers from
Control.Wire.Trans.Combine.  It is also pretty straightforward to write
your own wire transformers for this purpose.  You probably want to do
that later -- just look at the source code.
Greets,
Ertugrul
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